1. Field of the Invention
The present invention relates to a surface finishing agent for preventing metal surfaces from corrosion or for improving adhesion, particularly a novel imidazole-silane compound useful as a surface finishing agent for copper foils usable for copper-clad laminates for printed circuits, a process for producing it, and the use thereof.
2. Description of the Relates Art
The copper-clad laminates for printed circuits are produced by laminating a copper foil to a paper substrate impregnated with a phenolic resin or a glass substrate impregnated with an epoxy resin at an elevated temperature and pressure. It is then etched to form circuit patterns and elements such as semiconductor devices or the like are mounted thereon to form circuit boards for electronic devices. In the course of this process, the copper foil has to meet various requirements, since it is adhered to the substrate, heated, immersed in an acid or alkali solution, coated with a resist ink and soldered. For instance, excellent properties, such as adhesion to the substrate, resistance to chemical attacks or the like are mainly required on one side of the copper foil to be adhered onto the substrate. This side has been roughened and is generally called "M side" (matte side; hereinafter, similarly referred to). On the other hand, the other side (opposite to the M side) which is generally called "S side" (shiny side; hereinafter similarly referred to) must have heat resistance, moisture resistance, etc. Further, it is also required of both sides of the copper foil to be free from tarnishing due to oxidation during the storage.
To satisfy these requirements, a brass layer is formed on the M side of the copper foil (see Japanese Patent Publication Nos. 35711/1976 and 6701/1979), or the M side and S side are both treated with a chromate or coated with a zinc-chromium based mixture comprising zinc or zinc oxide and chromium oxide (see Japanese Patent Publication No. 7077/1983).
Recently, with the development of high-temperature heat-resistant resin substrates, higher heat resistance has been demanded for the S side of the copper foil. For example, the S side must be free from tarnishing due to oxidation in the range of from the conventional heating conditions of 200.degree. C..times.30 minutes to higher temperature heating conditions, such as 220.degree. C. or 240.degree. C..times.30 minutes. Also, in recent years, with a growing demand for finer patterns in printed wiring boards, further precise etching has become necessary. In order to satisfy such a demand, the M side is required to have a reduced surface roughness (i.e., low profile). However, on the other hand, roughening of the M side exhibits an anchoring effect in adhering the copper foil onto the substrate. Therefore, the requirement of low profile and the improvement in adhesion are incompatible with each other. If the anchoring effect is reduced due to low profile, the reduction of this effect should be compensated in a different manner to improve the adhesion.
It is also proposed to apply a silane coupling agent onto the M side, as a measure for strengthening the adhesion or as a countermeasure against the adhesion reduction due to the above-mentioned low profile (see Japanese Patent Publication No. 19994/1990 and Japanese Patent Laid-Open Nos. 183178/1988 and 26097/1990).
Known silane coupling agents usable for this purpose include vinyltriethoxysilane, vinyltris (2-methoxyethoxy)silane, 3methacryloxypropyltrimethoxysilane, 3glycidoxypropyltrimethoxysilane, 2-(3,4epoxycyclohexyl)ethyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2- (aminoethyl)-3-aminopropylmethyldimethoxysilane, 3aminopropyltrimethoxy, N-phenyl-3-aminopropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane and 3-chloropropyltrimethoxysilane [see "Koubunshi tenkazai no Saishingijutsu (The Latest Techniques of Polymer Additives)", pp. 120 to 134, published by C.M.C on Jan. 6, 1988.
However, as described above, since the printed circuits are more and more densified recently, the properties required of the copper foils for the printed circuits become more and more severe.